Human's spine includes cervical vertebrae, thoracic vertebrae, and lumbar vertebrae. A tailbone which is located at an end of the lumbar can cause serious pain if the user sits on the chair for a long time or does excessive labor.
Recently, as more time is spent on the chair at home and work, sitting on the chair in a correct posture becomes important. Pelvises are the most important part of a body balance since the pelvises support the spine and connect the spine and a lower body.
Also, dislocation of the pelvises causes thighs and calves to be bent, and therefore one must be careful of the pelvises. If a user with twisted pelvises sits on the chair for a long time, muscles and ligaments around the left and right are varied in tension, thereby causing pain and muscle stress. Also, it may cause backache and pelvic pain, and later lead to symptoms like thigh muscle stiffness or neck pain.
One example of a functional chair is disclosed in Korean Patent No. 10-0997074 (registered on Nov. 23, 2010), which includes a backrest, a base plate, armrests, legs, and supports for supporting the armrests. The functional chair further includes a posture correcting assembly having a plurality of springs spaced and arranged on a top surface of the base plate at regular intervals; a seat part having a first seat and a second seat which are divided in a direction of a butt's crack, and are connected to the springs to be moved in all directions according to loads applied to the first and second seats; a pair of moving parts which are provided with a slit extending on a bottom surface thereof in a longitudinal direction through which the supports pass, the armrest passing an inside of each moving part and being slidable in a forward and backward direction of the armrest; an elastic band of a desired width which is coupled to the pair of moving parts in a vertical direction from one side of an outer surface of the backrest and crosses the pair of moving parts, wherein the elastic band presses a user's waist such a way that the moving parts are slid to maintain lordosis of the lumbar vertebrae.
An example of a chair for correcting a pelvis is disclosed in Korean Utility Model No. 20-0256511 (registered on Nov. 24, 2001), which includes a seat part consisting of a pair of seats which are arranged at left and right sides and can be independently controlled in height; a support leg which is connected to a bottom surface of the seat part; and a backrest which is connected to the support leg at one side thereof.
As described above, the chairs for correcting the user's posture according to the related arts have a problem in that the seat part consisting of plural seat parts is separated from each other from side to side to disperse loads to be applied from left and right sides, but the loads to be applied from the left and right sides cannot be uniformly dispersed while keeping balance of a user's spine. That is, people having a bilaterally symmetric spine and left and right pelvises of the same level are up to 20% of the population, but the remaining populations of 80% should deform the shape of the chair to disperse his or her weight, according to his or her body type. If not, a load is applied to a specific portion of the body. In the case where a person stands at the position of attention or takes a fixed posture for one more hour, and this situation is repeated, it causes the backache and leads to the degenerative diseases in the spine and the pelvises.
In addition, a lordosis angle of the lumbar or a kyphosis angle of the thoracic vertebrae differs from individual to individual when the user bends his or her body back. Accordingly, since a backrest is fixed in a stationary shape, or the shape of a backrest is flexibly changed according to the degree of movement when the user bends the upper body back while sitting on the chair, based on average angles of the lordosis angle of the lumbar and the kyphosis angle of the thoracic vertebrae, there is a limit to taking a stable posture.
Furthermore, in the case where the backrest of the chair is tilted in a forward or rearward direction, heights of left and right back muscles are different from each other, but there is no product capable of compensating the height difference.